1. Field of the Invention
The present invention relates to purification of edible oils and in particular, triacylglycerol, more particularly, to a process for continuous purification of edible oils using an adsorbent material contained in one or more columns and regeneration of the adsorbent material for re-use.
2. Description of the Related Art
Animal and vegetable fats and oils are an essential and popular component of a healthy diet. These oils and fats provide essential nutrients and energy while making many other essential components of a healthy diet more palatable. In 2008 alone, the world-wide consumption of vegetable oils alone was almost 140 million short tons. These oils and fats must be refined in order to remove undesirable impurities that accelerate spoilage and reduce palatability and stability. Impurities to be removed include free fatty acids (FFA), metals, chlorophyll, and phosphatides and gums along with other trace compounds that reduce shelf-life, performance and palatability in the finished oil of fat.
A conventional edible oil refinery uses vast amounts of fresh water to refine its products and produces a corresponding amount of effluent requiring wastewater treatment or disposal into rivers, lakes, or other bodies of water. Additionally, the refinery uses substantial quantities of filter aid or treating media which once used requires disposal by landfill. It is desirable to utilize a process that minimizes the use of fresh water and treating media in order to reduce processing costs, effluent and solid waste.
Oils and fats, which are comprised of triacylglycerols (TAG), must be refined in order to remove undesirable impurities. During the processing of vegetable TAGs, extraction of crude TAG from the oilseed typically involves the use of a non-polar solvent. The conventional solvent most widely used for this process is hexane. Crude TAG is highly soluble in hexane thus allowing for a highly effective extraction of crude TAG from the oilseed. The resulting mixture of crude TAG and hexane can be separated, typically by distillation. The hexane is then recycled for reuse in the solvent extraction process while the crude TAG is further processed and refined by either a “Chemical Refining Process” or a “Physical Refining Process” as described below.
Regardless of the choice of refining method, the TAG should be “degummed” prior to moving forward with the process. The degumming process involves the use of water to remove water soluble phosphatides (gums) from the TAG. The water portion is removed from the TAG by centrifugation. General steps involved for each refining method are described below.
Chemical Refining Process:
A conventional process of chemical refining begins with a crude degummed triacylglycerol (TAG). The crude degummed TAG is subjected to an alkaline solution (typically, sodium hydroxide) to neutralize free fatty acids (FFA) and form a corresponding soap molecule (e.g., sodium oleate). These soaps are removed from the TAG. Centrifugation is used to remove some of the soaps. However, some of the soaps formed during the neutralization are not readily removed by this step and the residual soaps can be removed by further processing.
Residual soaps are removed via different methods. In a first conventional method, water wash is used to remove residual soaps: Since residual soaps are soluble in water, a series of water washing steps can be utilized to remove residual soaps from the TAG. This involves the addition of water to the TAG and soap mixture followed by centrifugation to separate and remove the soap-stock. While this process is efficient for removing the majority of the soaps from the TAG, there are still residual soap molecules remaining in the TAG that must be removed. In addition, there are other impurities present that are not water soluble and thus are not removed using the water washing method. Therefore, further processing of the TAG is required.
In a second conventional method, silica gel treatment using filtration is used to remove soaps from the TAG. The silica gel treatment method has been developed as an attempt to minimize waste effluent streams from the process. A silica gel is added to the TAG to remove soaps and it also removes metals that may be present. This process is highly efficient, but is done in batches, requires filtration, and can produce large amounts of waste filter cake requiring disposal.
Regardless of which conventional chemical refining method is chosen, the next step in the process is a bleaching step. During the bleaching step, the TAG is contacted with a bleaching clay to remove chlorophyll and other impurities that cause stability problems in finished TAG. Bleaching clays are traditionally used for this process due to their efficacy for removing chlorophyll pigments and other trace impurities present in the TAG. Bleaching clays can also remove residual soaps that may not have been removed during the previous processing step. The use of bleaching clay is typically done in batches, requires filtration, and results in large amount of waste filter cake requiring disposal.
The final step in the conventional chemical refining process involves subjecting the refined and bleached TAG to a deodorizing process. The deodorizing process uses steam and vacuum to remove any residual FFA and other volatile impurities that cause odor and color problems in finished TAG. The resulting finished oil from the process is referred to as refined, bleached, deodorized (RBD) TAG.
Conventional chemical refining processes include many variations of the above described methods, such as combining of the silica gel and bleaching clay treatments in one filtration cycle. This allows for faster processing of the TAG. Another conventional process uses a combination of water washing and silica treatment to displace one or more of the water washing steps. Conventional chemical refining of TAGs has the shortcoming of using large amounts of water and generating large amounts of waste effluent and/or solid filter cake waste, depending on the process used.
Physical Refining Process:
The conventional process of physical refining begins with a crude degummed triacylglycerol (TAG). The crude degummed TAG is first subjected to a bleaching clay and/or a silica gel to remove phosphorus compounds and other metals, chlorophyll and other contaminants that cause stability problems in TAGs. The physical refining process generates large amounts of solid filter cake waste that require disposal.
After the bleaching step, the TAG is subjected to the use of steam to remove the majority of FFA present in the TAG. Depending on the condition of the TAG, this step may be performed in a similar fashion to the deodorization step described above in the chemical refining process. If the TAG has a high FFA content, the use of steam to strip the majority of the FFA may be performed prior to a final deodorization step. The final TAG is referred to as refined, bleached, deodorized (RBD) TAG.
Conventional physical refining processes include many variations of the above described process. Conventional physical refining of TAG has the shortcoming of using large amounts of solid filter media and generating large amounts of solid waste requiring disposal.
Typically, whether a chemical refining or physical refining process is chosen depends on the condition of the crude degummed triacylglycerol (CDTAG). CDTAG that contains a high amount of FFA (>1.5%) is typically processed using physical refining. This is primarily because the risk of forming soap emulsion increases as the FFA content of a CDTAG increases. The more soap that is formed in the refining step, the greater the chance of emulsification, which results in increased processing difficulties and higher yield loss.
The following patents describe the use of an adsorbent to remove impurities from triacylglycerol compounds. U.S. Pat. No. 1,745,952 discloses a method for decolorizing fatty substances with adsorbents. U.S. Pat. No. 3,955,004 addresses a process for treating edible glyceride oil to improve color and storage properties using silica and aluminas. U.S. Pat. No. 2,401,339 describes a process to treat oils and waxes to remove impurities through the use of a solid adsorbent and distillation. U.S. Pat. No. 4,781,864 discloses a process for the removal of chlorophyll, color compounds and phospholipids using acid-treated silica type adsorbents.
U.S. Pat. No. 5,231,201, U.S. Pat. No. 5,248,799, U.S. Pat. No. 5,264,597, U.S. Pat. No. 5,928,639, U.S. Pat. No. 6,248,911, European Patent No. 0295418 B1, European Patent No. 0566224 A2, and U.K. Patent No. GB 2058121 A all relate to a process by which a refined glyceride oil is treated with an amorphous silica to remove impurities during chemical and/or physical refining.
U.K. Patent Application No. GB 2122588 A describes a process for regenerating spent adsorbents used for refining fatty materials, comprising contacting the spent adsorbent first with a polar organic solvent to remove adsorbed impurities and then with a non-polar organic displacing agent to remove the solvent adsorbed and reactivate the adsorbent.
None of aforementioned patents describe a complete system employing a continuous purification process using columns in combination with regeneration of the adsorbent. None of the prior art of which applicant is aware provides the feature of a continuous, regenerable adsorbent system that can be used to effectively and economically remove impurities when using chemical or physical refining methods. A purification system employing this feature is desirable in order to conserve and efficiently use scarce resources. Such a system dramatically reduces or eliminates the need for fresh water and the treatment or disposal or effluent and/or solid waste.
It is desirable to eliminate batch processing and provide a continuous process for the purification of edible oils. It is also desirable to provide an environmentally friendly “green” process that greatly reduces or eliminates the large volumes of fresh water conventionally required and waste water produced to refine edible oils and fats, as well as, the energy and space required to produce, transport, and landfill solid waste. It is further desirable to provide a process that once charged with an adsorbent comprises a closed system requiring no fresh water or new adsorbent for operation while generating no effluent or solid waste that needs to be treated or disposed of.